With advances in compactification and increased density in semiconductors, such as LSIs, particular progress has been made in recent years in compactification and increased density in the thickness direction of semiconductor devices, by three-dimensional mounting, for instance. In conjunction with this, in a step for manufacturing a semiconductor device, reverse surface processing is carried out to process the reverse surface on the opposite side to the front surface on which the device is formed, for instance, a step for reducing the thickness of the semiconductor wafer. Furthermore, also in a power device such as an IGBT, MOSFET or diode, which is mounted on an inverter circuit or uninterrupted power source device, etc. which is used for driving an industrial or automobile motor, a thickness reduction step is carried out on the semiconductor wafer, in order to improve the activation performance, such as the on characteristics. Moreover, forming an impurity layer or reverse surface electrode, etc. is also carried out as reverse surface processing.
In general, after first carrying out mechanical polishing of the reverse surface side as a reserve surface process on the semiconductor wafer, a semiconductor wafer thickness reduction process is carried out by chemical etching using a chemical liquid in order to remove stress and fractured layers from the polishing. As a pre-process for this step, a surface protection film is formed in order to protect the device on the front surface side from scratches and chemical liquid. The chemical etching process after the mechanical polishing is carried out by rotary wafer etching in which chemical liquid is supplied to one side only, while rotating the semiconductor wafer.
However, due to the surface tension of the chemical liquid, the chemical liquid also flows around to the outer peripheral section of the surface on the opposite side to the etching process surface, and the chemical liquid penetrates in between the surface of the semiconductor wafer and the protection film. Consequently, there is a problem in that the protection film in the outer peripheral section detaches, and the yield rate of the device declines due to conveyance errors and processing defects of the semiconductor wafer in post-processing, and scratching of the device surface and corrosion by the chemical liquid.
In order to avoid corrosion of the surface by the chemical liquid, it has been proposed that the diameter of the surface protection film be made larger than the device surface and smaller than the diameter of the periphery of the semiconductor wafer (see, for example, PTL 1).